The invention relates to an electro optic voltage sensor, comprising means for producing an incident light wave, an electro optic transducer presenting a 2nd order non-linear electro optic effect arranged in an electrical field generated by a voltage to be measured and comprising an input receiving the incident light wave and an output supplying an output light wave, insulating means supporting the transducer, means for opto-electronic detection connected to the output of the transducer, and electronic processing means connected to the means for detection.
The field of non-linear optics involves the non-proportional response of light interacting with matter. A 2nd order non-linear effect is well known wherein wave-mixing of different light frequencies merge to produce other frequencies. Two examples of the 2nd order non-linear effect are the Second Harmonic Generation effect, wherein wave-mixing of two equal fundamental frequencies yield a second harmonic frequency, and the Pockels effect wherein a fundamental frequency is mixed with a d.c. element to change the refractive index of light passing through a material. A Pockels effect linearly advances or retards the refractive index of light waves in a manner directly proportional to the intensity of an applied electric field.
Known electro optic voltage sensors generally use as transducer a crystal sensitive to the electrical field. Such crystals present a 2nd order non-linear electro optic effect, of the Pockels effect type. The galvanic isolation is limited by the small dimensions of the transducer crystal, typically about one centimeter. These sensors are consequently not suitable for measuring very high electrical voltages, of several hundred kilovolts for example. For reasons of dielectric strength of the transducer material, it is not possible to apply the whole voltage to be measured to the terminals of the crystal. For measuring high voltages, sensors of this type are consequently combined with voltage dividers.
An electro optic sensor for measuring a voltage at 345 kV without a voltage divider has been described in the article "Application of an electro optic voltage transducer at 345 kV" presented at "EPRI, Optical sensors for Utility T & D Applications Workshop, Portland, Oreg., Jul. 20-21, 1995". In this sensor, the transducer is formed by a special crystal, of large dimensions, presenting a longitudinal electro optic effect. A crystal of large dimensions is costly and the insulation distance of the head of the sensor is equal to the size of the transducer crystal, which requires a complex and costly implementation to achieve the dielectric strength of the sensor in a high voltage environment.